Disclaimer: I used to work on Thunderbird support, but I haven't worked on Thunderbird since 2012. I know nothing about the code; I still use Thunderbird daily but I won't be heart broken if/when Thunderbird in its present form ceases to exist; I will just use something else! And like many others I pay Thunderbird a small amount of money to hopefully keep it going and to fund Thunderbird.next whatever that turns out to be!